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Volume 17 Issue 12
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Original Articles
Realization of the Three-Qubit Toffoli Gate in Molecules
DU Jiang-Feng, SHI Ming-Jun, ZHOU Xian-Yi, FAN Yang-Mei, WU Ji-Hui, YE Bang-Jiao, WENG Hui-Min, HAN Rong-Dian,
Chin. Phys. Lett. 2000, 17 (12): 859-861 .  
Abstract   PDF(pc) (280KB) ( 554 )
We present the experimental realization of this gate with a solution of chlorostyrene molecules. Our method does not depend heavily on the two-qubit controlled operation, which used to serve as the basic quantum operation in quantum computing. At present, we use transition operator that can be applied to all qubits in one operation. It appears that no experimental realization has yet been reported up to now regarding the implementation of quantum Toffoli gate using transition pulse on three-qubit nuclear magnetic resonance quantum computers. In addition, our method is experimentally convenient to be extended to more qubits.
Quantum Dynamical Theory for Squeezed Atom Laser
JING Hui, HAN Yi-Ang, CHEN Jing-Ling, MIAO Yuan-Xiu
Chin. Phys. Lett. 2000, 17 (12): 862-864 .  
Abstract   PDF(pc) (201KB) ( 404 )
A model for the squeezed output coupler of the trapped Bose-Einstein condensed atoms is established with a simple many-boson system of two states with linear coupling, by preparing an initially squeezed light field. In the Bogoliubov approximation, its solutions show that the quadrature squeezing effect mutually oscillates between the coupling light field and the output atomic field. This manifests that the initially squeezed light will transform into a coherent state after some period of coupling interaction while the output atomic field is in a squeezed state.
A Twist-4 Effect in the Parton Evolution Processes
RUAN Jian-Hong, ZHU Wei, LI Guang-Lie,
Chin. Phys. Lett. 2000, 17 (12): 865-867 .  
Abstract   PDF(pc) (210KB) ( 395 )
Recently, a research group reported that they can fit the F2 data well by using the Altarelli-Parisi evolution equation with a valence-like initial gluon distribution, which means that we need not consider the high twist effects in the proton. In this letter, we point out that their valence-like initial gluon distribution is unreasonable for the proton structure function. With the reasonable initial distributions, we find that the high twist corrections to the Altarelli-Parisi evolution equation is necessary.
Some Comments on the Frame of Regge Phenomenology and the Glueball Production Mechanism
PENG Hong-An, XU Jia-Sheng
Chin. Phys. Lett. 2000, 17 (12): 868-870 .  
Abstract   PDF(pc) (251KB) ( 354 )
We enumerate the limitations in the frame of Regge phenomenology and demonstrate that it should be extended to cover the freedom of constituent gluon, We declare that glueballs are the bound states of constituent gluons. Based on these observations we discuss the glueball production mechanism and the structure of Pomeron.
Microscopic Mechanism of the Odd-Even Difference in Moments of Inertia of Superdeformed Bands
LIU Shu-Xin, YU Lei, ZENG Jin-Yan
Chin. Phys. Lett. 2000, 17 (12): 871-873 .  
Abstract   PDF(pc) (254KB) ( 419 )
The large odd-even difference in moments of inertia between the SD bands l95Tl(l,2) and l96Pb(l) is investigated by the particle-number conserving method, in which the blocking effect on pairing is taken into account strictly. The ω variation of J(2) for the three SD bands are reproduced quite well and the underlying microscopic mechanism is demonstrated clearly. Calculations show that the blocking of the proton [642]5/2 intruder orbital and the excitation of [651]1/2 intruder orbital play crucial roles for the odd-even difference in J(2)’s.
Strange Hadronic Matter in a Chiral Model
ZHANG Li-Liang, SONG Hong-Qiu, WANG Ping, SU Ru-Keng
Chin. Phys. Lett. 2000, 17 (12): 874-876 .  
Abstract   PDF(pc) (276KB) ( 309 )
The strange hadronic matter with nucleon, Λ-hyperon and Ξ-hyperon is studied by using a chiral symmetry model in a mean-field approximation. The saturation properties and stabilities of the strange hadronic matter are discussed. The result indicates a quite large strangeness fraction (fs) region where the strange hadronic matter is stable against particle emission. In the large fs region, the Ξ component dominates, resulting in a deep minimum in the curve of the binding energy per baryon EB versus the strangeness fraction fs with (EB, fs) ~_ (-26.0MeV,1.23).
Ion-Induced Beam Instability in an Electron Storage Ring
LI Yong-Jun, JIN Yu-Ming, LI Wei-Min, LIU Zu-Ping
Chin. Phys. Lett. 2000, 17 (12): 877-878 .  
Abstract   PDF(pc) (166KB) ( 320 )
In a small electron storage ring, such as the Hefei Light Source (HLS) ring, the newly generated ions, which can not escape from the beam potential and then are trapped from turn to turn, will lead to the beam instability. The ions created by the leading bunches can perturb the trailing bunches and also themselves during their subsequent passage, which will make the amplitude of beam oscillation be damped and anti-damped periodically. A computer simulation based on the strong-weak model shows a good agreement with our analytical model using the linear theory.
High Order Centrifugal Distortion Corrections to Energy Levels of Asymmetric Top Molecules
LIU Yu-Yan, LIU Xiao-Yong, LIU Hong-Ping, GUO Yuan-Qing, HUANG Guang-Ming, LIN Jie-Li, GAO Hui
Chin. Phys. Lett. 2000, 17 (12): 879-881 .  
Abstract   PDF(pc) (216KB) ( 399 )
High order centrifugal distortion terms have been derived and added to the effective Hamiltonian of asymmetric top molecules. Based on this Hamiltonian, a program in Fortran 77 has been developed for spectral analysis of asymmetric top molecules. The high order centrifugal distortion terms are found to be non-negligible even for the low-lying rotational transitions of molecules, such as H218O, subjected to severe centrifugal distortion effect, and for the high-lying rotational transitions of molecules, such as 14N16O2 subjected to the moderate centrifugal distortion effect.

Proposal for Direct Measurement of the Wigner Function of a Cavity Field via Raman Coupling
ZHENG Shi-Biao, ZHU Xi-Wen
Chin. Phys. Lett. 2000, 17 (12): 882-884 .  
Abstract   PDF(pc) (220KB) ( 384 )
We propose a scheme for the reconstruction of a cavity field state. In the scheme the cavity field is first displaced by a microwave source, and then couples with a three-level A-type atom in a Raman manner. After an appropriate interaction time the measurement of the difference between the probabilities of the atom being in two ground states directly yields the Wigner function for the field state. The scheme can be easily generalized to measure the Wigner function of an entangled state of two spatially separated single-mode cavities.
Quantum Entropic Dynamics of a Trapped Ion in a Standing Wave
FANG Mao-Fa, ZHOU Peng, S. Swain
Chin. Phys. Lett. 2000, 17 (12): 885-887 .  
Abstract   PDF(pc) (247KB) ( 631 )
By performing a unitary transformation, we transform the Hamiltonian of the trapped ion in any position of standing wave to that of the normal Jaynes-Cummings model in ionic bare basis and we obtain a general evolution operator of the trapped ion system. We study the quantum entropic dynamics of the phonons and trapped ion.Our results show that, when the trapped ion is located at the node of standing wave, the quantum entropic dynamics of phonons and trapped ion are the same as the one of the field in the Jaynes-Cummings model. When the trapped ion deviates from the node of standing wave, the entropies of the phonons and ion keep their maximum value except at the initial stage, and the phonons and trapped ion become extremely entangled.
High Efficient Laser Operation of the Nd:KGd(WO4)2 Crystal Grown by Flux Method
LUO Zun-Du, CHEN Xue-Yuan, TU Chao-Yang, J. J. Romero, J. Garcia Sole
Chin. Phys. Lett. 2000, 17 (12): 888-889 .  
Abstract   PDF(pc) (175KB) ( 330 )
The laser performance of Neodymium-doped potassium gadolinium tungstate (Nd:KGd(WO4)2) crystal was studied by using Ti:Sapphire laser as the pump source. The maximum optical-to-optical efficiencies for the 1.067 and 1.3 μm laser outputs were measured to be 60% and 32.3%, respectively. The internal loss coefficient of the crystal for 1.067 μm laser was estimated to be as low as 0.004 cm-1. The oscillation thresholds at 1.067 and 1.3 μm for different output transmittances are also given.
Dust-Acoustic Waves in Strongly Coupled Dusty Plasmas Containing Variable-Charge Impurities
XIE Bai-Song, , HE Kai-Fen, , M. Y. Yu
Chin. Phys. Lett. 2000, 17 (12): 890-892 .  
Abstract   PDF(pc) (261KB) ( 461 )
A relatively self-consistent theory of dust-acoustic waves in the strongly coupled dusty plasmas containing variable-charge impurities is given. Relevant physical processes such as dust elastic relaxation and dust charge relaxation are taken into account. It is shown that the negative dispersion of dust-acoustic waves due to the strong correlation of dusts is enhanced in the presence of dust-neutral collisions.
Parameter Processes of a Strong Laser in Partially Stripped Plasmas
HU Xi-Wei
Chin. Phys. Lett. 2000, 17 (12): 893-895 .  
Abstract   PDF(pc) (216KB) ( 569 )
The effects of the nonlinear polarization in a partially stripped plasma on the parameter processes of a strong laser are discussed. The nonlinear mode coupling equations of stimulated Raman scattering (SRS) are derived. The linear instability growth rates of SRS and stimulated Brillouin scattering (SBS) are given. When the pump wave intensity I0 > 1017 W/cm2, the third order susceptibility associated with bound electrons will reduce the SRS and SBS linear growth rate enormous1y. In addition, the nonlinear susceptibility can affect the nonlinear evolution of SRS and SBS significantly.
BO2-F+ Centers in the Radiation-damaged YCOB Crystals
RUAN Yong-Feng, Hiroshi NAKAO, Takatomo SASAKI
Chin. Phys. Lett. 2000, 17 (12): 896-898 .  
Abstract   PDF(pc) (264KB) ( 512 )
An intense paramagnetic EPR signal generated from x-ray-irradiated, powdered YCOB crystals was observed at the liquid nitrogen temperature for the first time. Five peaks, located at the positions where the effective g factor equals to 1.992, 1.986, 1.980, 1.974 and 1.965, labeled as A, B, C, D and E respectively, were observed. It is believed that the peaks A, B, C and D generated from the BO2-F+ center which is a single electron trapped in an oxygen vacancy which was originally occupied by an O2- ion bonded to a (BO3)3- anion group. The peak E is thought of coming from Y2+ ions that are formed by the Y3+ ions trapping electrons. The mechanism for the formation of the radiation-induced defects in the YCOB crystals is suggested.
Asymmetry Localized Modes in an Anharmonic Sphalerite-Structure Lattice
ZHOU Guang-Hui, XIA Qing-Lin, PAN Liu-Xian, YAN Jia-Ren
Chin. Phys. Lett. 2000, 17 (12): 899-901 .  
Abstract   PDF(pc) (262KB) ( 387 )
We numerically study the intrinsic localized vibrational modes in a diatomic chain with different masses and alternating force constants between nearest neighbors. This model simulates a row of atoms in the <111> direction of sphalerite-structure crystal. We found that the harmonic and quartic anharmonic terms in the nearest-neighbor interaction potential produce the intrinsic localized modes with frequencies above the optical branch or in the gap of the linear spectrum, the distribution patterns of atom amplitudes are asymmetry with a form of quasi-even- or quasi-odd-parity, and the inclusion of cubic term in the potential lowers the frequencies of the modes and introduces static displacements for the atoms.

Tunneling Time of Particles Through a Potential Barrier
LI Chun-Fang, WANG Qi
Chin. Phys. Lett. 2000, 17 (12): 902-904 .  
Abstract   PDF(pc) (249KB) ( 443 )
A new tunneling time is proposed by introducing the transfer speed of energy carried by tunneling particles. This speed is similar to the energy transfer speed in electromagnetism, and with the tunneling time, the well-known superluminality may be avoided. The low energy limit, the critical limit, and the opaque limit are considered, which are physically meaningful. Comparisons with dwell time and Biittiker and Landauer’s semiclassical time are also made.
Néel Transition and Staggered Magnetization of La2-δSrδCuO4
Chin. Phys. Lett. 2000, 17 (12): 905-906 .  
Abstract   PDF(pc) (180KB) ( 440 )
The doped anisotropic antiferromagnet, which is believed to describe the elementary properties of the high-temperature superconductors, is studied by making use of Green’s function theory of the t-J model. The Néel transition and staggered magnetization dependence on the anisotropic parameter ς and the doping density δ in La2-δSrδCuO4 are obtained. These results are found to be in good agreement with experiments on the cuprates.

New Resistance Anomaly in Superconducting Bi2Sr2CaCu2O8 Single Crystals
WANG Wen-Hu, ZHOU Yu-Qin, CHEN Zhao-Jia, ZHENG Ping, JIN Duo, WANG Yu-Peng
Chin. Phys. Lett. 2000, 17 (12): 907-908 .  
Abstract   PDF(pc) (195KB) ( 312 )
We have measured the resistance of some Bi2Sr2CaCu2O8 superconducting single crystals along ab plane and the c axis. For some of the single crystals, a resistivity anomaly near the superconducting transition temperature is observed in the ab plane. This giant resistance peak is independent of the small driving current (I ≤40 mA), and the peak is suppressed and vanished gradually with the increasing applied magnetic field (> 100 G). We proposed that the resistance peak is a quasi-reentrant behavior due to the superconducting phase inhomogeneous distribution.
Monte Carlo Simulation of Light Transport in Five-Layered Skin Tissue
XUE Ling-Ling, ZHANG Chun-Ping, WANG Xin-Yu, ZHU Ming-Yao, ZHANG Lian-Shun, CHI Rong-Hua, ZHANG Jian-Dong, ZHANG Guang-Yin
Chin. Phys. Lett. 2000, 17 (12): 909-911 .  
Abstract   PDF(pc) (247KB) ( 652 )
The light propagation and distribution in skin tissue is studied by using Monte Carlo technique. The radially resolved diffuse reflectance R and transmittance T vs radius r , angularly resolved R and T vs the exiting angle of the photon, absorption energy density A and internal Auence F vs r and z are simulated. Our results reveal that the light distribution for Gaussian beam is more centralized and its change is more rapid than those of circularly flat beam under the same incident energy and radius, no matter what R and T or A and F are. In addition, except that R(r) for circularly flat beam needs to be fitted by 15-order curve, the others can be fitted by 5-order or 6-order curve.
FTIR Characterization of Fluorine Doped Silicon Dioxide Thin Films Deposited by Plasma Enhanced Chemical Vapor Deposition
WANG Peng-Fei, DING Shi-Jin, ZHANG Wei, ZHANG Jim-Yun, WANG Ji-Tao, WEI William Lee
Chin. Phys. Lett. 2000, 17 (12): 912-914 .  
Abstract   PDF(pc) (262KB) ( 1578 )
Fluorine doped silicon dioxide (SiOF) thin films have been prepared by plasma enhanced chemical vapor deposition. The Fourier transform infrared spectrometry (FTIR) spectra of SiOF films are deliberated to reveal the structure change of SiO2 and the mechanism of dielectric constant reduction after doping fluorine. When F is doped in SiO2 films, the Si-O stretching absorption peak will have a blue-shift due to increase of the partial charge of the O atom. The FTIR spectra indicate that some Si-OH components in the thin film can be removed after doping fluorine. These changes reduce the ionic and orientational polarization, and result in the reduction in dielectric constant of the film. According to Gaussian fitting, it is found that the Si-F2 bonds will appear in the SiOF film with increase of the fluorine content. The Si-F2 structures are liable to react with water, and cause the same increase of absorbed moisture in the film.

High Current Gain In0.49Ga0.51P/GaAs Heterojunction Bipolar Transistors with Double Spacers Grown by Gas Source Molecular Beam Epitaxy
CHEN Xiao-Jie, CHEN Jian-Xin, CHEN Yi-Qiao, PENG Peng, YANG Quan-Kui, LI Ai-Zhen
Chin. Phys. Lett. 2000, 17 (12): 915-917 .  
Abstract   PDF(pc) (259KB) ( 449 )
This paper reports the improved performance of the lattice-matched N-p+-n In0.49Ga0.51P/GaAs heterojunction bipolar transistors(HBTs) with undoped spacers grown by the gas source molecular beam epitaxy. A 600 Å GaAs base doped with beryllium at 3 x 1019cm-3 and a 1000 Å In0.49Ga0.51P emitter doped with silicon at 3 x 1017cm-3 have been grown. On both sides of the base, the 50 Å undoped GaAs spacers were grown. Devices with emitter area of 100 x 100 μm2 were fabricated by using selective wet chemical etching technique. The measured results of HBTs reveal cood junction characteristics, and the common-emitter current gain reaches 320 at the collector current density of 280 A/cm2.
Thermodynamic Equilibrium Studies of Nanocrystallite CeO2 Grain Boundaries by High Temperature X-Ray Photoelectron Spectroscopy and Thermal Gravimetric Analysis
LIU Zhen-Xiang, XIE Kan
Chin. Phys. Lett. 2000, 17 (12): 918-920 .  
Abstract   PDF(pc) (247KB) ( 311 )
Nanostructured CeO2 thin films and powders are studied by high temperature x-ray photoelectron spectroscopy and thermal gravimetric analysis. The results indicate that the surface composition strongly depends on temperature, the surface O/Ce ratio initially increases with increasing temperature, then decreases with the further increase of temperature, the maximum surface O/Ce ratio is at about 300°C. The variation of the surface composition with temperature arises from the ion migration, redistribution and transformation between lattice oxygen and gas phase oxygen near the grain boundaries during the thermodynamic equilibrium process. The results also show that CeO2 has a weakly bond oxygen, high oxygen mobility in the bulk and a high molecular dissociation rate at the surface, especially for the sol-gel prepared nanocrystallite CeO2.
Demonstration of Far-Infrared GaAs/AlGaAs Quantum Well Photodetectors for Broadband Wavelength Detection
SHEN Wen-Zhong, Perera A. G. U.
Chin. Phys. Lett. 2000, 17 (12): 921-923 .  
Abstract   PDF(pc) (308KB) ( 658 )
We discuss the realization of broadband wavelength detection by demonstrating the longest cutoff wavelength (λc = 28.6 μm) far-infrared GaAs/AIGaAs quantum well infrared photodetectors (QWIPs). The responsivity is comparable to that of mid-infrared GaAs/AIGaAs and InGaAs/GaAs QWIPs, with a responsivity of 0.265 A/W and detectivity of 3.4x109 cm.Hz1/2/W at the peak wavelength of 26.9μm at 4.2K. Based on the temperature-dependent dark current and response results, it is expected that similar performance can be obtained at least up to 20 K. Several ways to expand the wavelength coverage are also addressed.
A New Method for Experimental Determination of Compressional Velocities in Rocks and Minerals at High-pressure
LIU Yong-Gang, XIE Hong-Sen, GUO Jie, ZHOU Wen-Ge, XU Ji-An, ZHAO Zhi-Dan
Chin. Phys. Lett. 2000, 17 (12): 924-926 .  
Abstract   PDF(pc) (269KB) ( 478 )
A transmission-reflection-combined new method is presented for measuring elastic velocities of rocks and minerals at elevated temperature and pressure, which resolves the problems of gradients of temperature and pressure existing in original sample assembly with a pyrophyllite cube. At room temperature and pressure up to 3 GPa, single-crystal quartz and eclogite were used to provide samples under test, respectively. The results of this work agree with the previous measurements very well within the error range. By the use of this new technique, more precise and reasonable data of elastic properties of rocks and minerals at elevated temperature and pressure can be achieved.
Diagnostics of Magnetic Field Strength in Gyrosynchrotron Radiation Regions for the Case of Transverse Propagation
ZHOU Ai-Hua, WANG Xin-Dong
Chin. Phys. Lett. 2000, 17 (12): 927-928 .  
Abstract   PDF(pc) (153KB) ( 384 )
A set of diagnostic formulas is, for the first time, proposed to deal with the magnetic field strength B in gy-rosynchrotron radiation regions for the transverse propagation case. The diagnostic formulas of B are applied to analyze a solar limb event. The differences of diagnostic results of B are compared for the different propagation cases and it is found that the differences are rather large. So in the analysis of limb burst we should use the diagnostic formulas for the transverse propagation.
Group Velocity of the Density Waves in Galactic Disks
LONG Min, PENG Qiu-He, LUO Xin-Lian, CHOU Chih-Kang
Chin. Phys. Lett. 2000, 17 (12): 929-931 .  
Abstract   PDF(pc) (237KB) ( 328 )
This letter is emphasized on the discussion of the group velocity of disturbed galactic density waves (GDW), which is one of the two most insurmountable problems in the density waves theory. In our calculation, we find that the galactic thickness has an important effect on the GDW. The dynamic time scale of GDW in our three-dimensional model can be prominently prolonged, from 36% to 60% contrasting to that of two-dimensional galactic model. However, it is still less than the lifetime of our Galaxy, which means that it is necessary to seek some other physical mechanisms to excite and sustain the GDW.
On Three-Dimensional Spiral Galaxies
LUO Xin-Lian, PENG Qiu-He, LONG Min, PENG Fang, ZOU Zhi-Gang
Chin. Phys. Lett. 2000, 17 (12): 932-934 .  
Abstract   PDF(pc) (262KB) ( 465 )
Density waves in 3D spiral galaxies are studied. In order to eliminate the forbidden region near the corotation in the grand-design galaxies, we assume that the perturbation satisfies the stable condition Q(r) > 1 over all the disk except that at the corotation. Then, a new method is put forward here to determine some basic parameters of spiral galaxies. We apply it to our Galaxy, and the results are in good agreement with the previous results.
Physical Background of the Unified Scaling Law in Spiral Galaxies
ZOU Zhen-Long, HAN Jin-Lin
Chin. Phys. Lett. 2000, 17 (12): 935-936 .  
Abstract   PDF(pc) (177KB) ( 437 )
We discussed the physical background of the unified scaling law in spiral galaxies, and qualitatively obtained the power index of the empirical relation among the luminosity L, radius R and the rotation velocity V. We also discussed the possible causes for the data dispersion on the plane in three-dimensional space of these parameters.
28 articles